We continue to investigate the mechanism of insulin action in developing skeletal muscle as it promotes increases in glucose utilization. During these studies we have devised a new cell culture technique for skeletal muscle cells using micro carriers. In other studies, using monolayer cultures in dishes, we have devised the conditions wherein differentiated muscle cells respond to physiological concentrations of insulin in promoting increased glucose utilization. This is a significant finding because all previously reported studies necessitated the use of superphysiological insulin concentrations. We are now in a position to study the mechanism of insulin action and determine whether modification of insulin receptor-effector interaction involves changes in sulfhydryl groups.